This invention relates to rack and pinion steering devices employing rack bar supports having rollers. In rack and pinion steering gears, a rack bar transverses along its axis when the pinion, which has teeth meshing with the teeth of the rack bar, is turned by the steering wheel and column assembly. Commonly, a support yoke biases the rack bar, toward the pinion to maintain the desired meshing of the rack teeth with the pinion teeth during rotation of the pinion. The support yoke also reacts against shock loads transmitted to the rack bar from bumps in the road via the vehicle wheels, suspension and steering system tie rods.
In light vehicles, such as passenger cars, the rack bar is engaged by a yoke engaging surface complimentary in shape to the section of the rack bar. Friction between the rack bar and the support yoke engaging surface can be reduced by applying low friction surface coatings to the yoke engaging surface. Minimization of friction between the support yoke and the steering rack is an important factor in achieving good steering feel.
Heavier vehicles, such as full sized pick-up trucks and medium duty commercial vehicles, because of their greater mass, have yoke-to-rack bar interface loads of greater magnitude than light vehicles, and consequently have higher associated steering friction loads. One means of reducing the friction load between the rack bar and the yoke support is to locate a roller within the yoke for engagement with the rack bar. Typically, the roller is of a curved profile, complementary in shape to the generally cylindrical rack bar. The roller fits between two walls of the yoke and may have thrust washers disposed between itself and the yoke. Known yoke and roller assemblies, however, are subject to a small amount of fore-aft axial play or movement, as the stack-up tolerances of the assembled components make it extremely difficult to provide a line-to-line fit of the parts. Even a small amount of axial play is undesired as it can be detected by the vehicle operator as an unwanted vibration which may be perceived as an indicator of poor quality. While parts can be made to very close manufacturing tolerances and carefully selected to provide assemblies having little or no axial play, eliminating the play through dimensional control and part selection is expensive. A spring load between each end of the roller and the support yoke can be used to cushion but not eliminate all axial play.
It is desired to provide a steering gear having a low friction rack bar roller support which eliminates the axial play of the roller, is insensitive to slight variations in the roller and yoke components dimensions, and is easy to assemble.